Conventionally, widely used is a card reader for a magnetic recording medium processing device which reads magnetic data recorded on a magnetic recording medium in a card form (hereinafter called “a card”) and/or writes magnetic data on a card. A card reader of this kind is installed and used in a host device such as an ATM (Automated Teller Machine) which is set up at a financial institution such as a bank. In recent years, in the industry of the financial institution where card readers are used, a so-called “skimming”, which means that a fraudster attaches a magnetic head to the front of a card insertion opening of a card reader to illegally acquire magnetic data of cards, has been a serious problem.
Therefore, a card reader equipped with a magnetic field generating device has been proposed, the magnetic generating field generating device generating a disturbing magnetic field to disturb the reading of magnetic data on cards by a skimming magnetic head attached to the front of a card insertion opening (Patent reference 1, for example). The card reader disclosed in Patent reference 1 is equipped with a magnetic field (magnetism) generating device which is mounted at a card insertion opening of the card reader and has a technology to disturb the skimming magnetic head from reading magnetic data of a card user with a disturbing magnetic field released from the magnetic field (magnetism) generating device.
In this technology, a circuit that generates a disturbing magnetic field has adopted the configuration to turn on the power source of a coil (an inductor) with a transistor having a switching function.
In the card reader disclosed in Patent reference 1, the above-mentioned magnetic field (magnetism) generating device is applied in the following manner. A fraudster attaches a skimming magnetic head, which is a magnetic head, and a magnetic reading circuit at the card insertion opening of a card reader to read magnetic data on cards. To prevent the skimming magnetic head from reading magnetic data, a disturbing magnetic field is generated toward the skimming magnetic head.